Thursday, October 28, 2010

Fossil Fish With "Limbs" Is Missing Link, Study Says

Fossil hunters may have discovered the fish that made humans possible.

Found in the Canadian Arctic, the new fossil boasts leglike fins, scientists say. The creature is being hailed as a crucial missing link between fish and land animalsincluding the prehistoric ancestors of humans.

Researchers say the fish shows how fins on freshwater species first began transforming into limbs some 380 million years ago. The change was a huge evolutionary step that opened the way for vertebratesanimals with backbonesto emerge from the water.

"This animal represents the transition from water to landthe part of history that includes ourselves," said paleontologist Neil Shubin of the University of Chicago.

Shubin was co-leader of a team that uncovered three nearly complete fossils measuring up to nine feet (three meters) long on Ellesmere Island in 2004.

The new species, Tiktaalik roseae, had a flattened, crocodile-like head and strong, bony fins.

The large fish probably flexed and extended these fins like legs to help it move through shallow, subtropical waters or even on land, the team says.

The discovery marked the culmination of a five-year, 400-mile (650-kilometer) fossil hunt across the Arctic's frozen tundra. The National Geographic Society partially funded the project, which is to be detailed tomorrow in the journal Nature.

The fish shows other features characteristic of land animals, including ribs, a neck, and nostrils on its snout for breathing air.

The previously unknown creature is the closest known fish ancestor of land vertebrates, Shubin said.

It likely used its fins "to prop its body, much like we do when we do a push-up," he said.

Likewise, the animal's broad ribs would have supported its long, scaly trunk, adds team member Farish Jenkins of Harvard University in Cambridge, Massachusetts.